Błąd w parsowaniu daty pobranej z API

public class WorkTimeModel
    {
        public Guid Id { get; set; }
        [JsonProperty("ApplicationUser")]
        public ApplicationUser User { get; set; }
        public DateTime StartTime { get; set; }
        public DateTime? EndTime { get; set; }
        public ePlaceType PlaceType { get; set; }
        [JsonProperty("PlaceCar")]
        public Place_CarModel Car { get; set; }
        [JsonProperty("PlaceOffice")]
        public Place_OfficeModel Office { get; set; }

        public double GetWorkTimeProgressProcentage(TimeSpan WorkTime)
        {
            DateTime maxWorkDate = StartTime.AddTicks(WorkTime.Ticks).AddTicks(-StartTime.Ticks);
            DateTime now = DateTime.Now.AddTicks(-StartTime.Ticks);
            return (now.Ticks * 100) / maxWorkDate.Ticks;
        }
    }

{
    "Success": true,
    "Error": "",
    "Data": {
        "Id": "ed34302e-efef-454c-9afa-5e1d93863bfb",
        "ApplicationUserId": "782wcea0-29bc-4167-a820-7d7cbe010154",
        "ApplicationUser": {
            "Id": "782wcea0-29bc-4167-a820-7d7cbe010154",
            "Login": "login",
            "Password": "haslo",
            "FirstName": "Jan",
            "LastName": "Kowalski",
            "Roles": "{\"Values\":[\"Technician\",\"Officeman\",\"Warehouseman\"]}",
            "Token": "56w6a2f4-862d-4d27-a673-610g8301cfba",
            "IsDeleted": false
        },
        "StartTime": "2021-11-08T12:36:55.6649463",
        "EndTime": null,
        "PlaceType": 0,
        "PlaceCarId": "70686183-1659-4fb2-9775-052e6bc59429",
        "PlaceCar": {
            "Id": "70686183-1659-4fb2-9775-052e6bc59429",
            "PlaceName": "Opel Astra",
            "RegistrationNumber": "GDA LD908",
            "QrCode": "car1"
        },
        "PlaceOfficeId": null,
        "PlaceOffice": null
    }
}

CurrentWorkTime = await workTimeService.GetCurrentWorkTime(CurrentUser);
if (CurrentWorkTime != null && !CurrentWorkTime.EndTime.HasValue)
     StartWorkTimer();

public void StartWorkTimer()
        {
            UpdateWorkTimeProgressBar();
            Device.StartTimer(new TimeSpan(0, 0, 30), () =>
            {
                if (CurrentWorkTime != null && !CurrentWorkTime.EndTime.HasValue)
                {
                    StartWorkTimer();
                }
                return false;
            });
        }

public void UpdateWorkTimeProgressBar()
        {
            if(CurrentWorkTime != null)
            {
                double progress = CurrentWorkTime.GetWorkTimeProgressProcentage(new TimeSpan(0, 10, 0));
                WorkTimespanProgress = (float)progress / (float)100.00f;
            }
        }

public double GetWorkTimeProgressProcentage(TimeSpan WorkTime)
        {
            Debug.WriteLine($"GetWorkTimeProgressProcentage - maxWorkDate");
            DateTime maxWorkDate = StartTime.AddTicks(WorkTime.Ticks).AddTicks(-StartTime.Ticks);
            Debug.WriteLine($"GetWorkTimeProgressProcentage - now");
            DateTime now = DateTime.Now.AddTicks(-StartTime.Ticks);
            Debug.WriteLine($"GetWorkTimeProgressProcentage - return");
            return (now.Ticks * 100) / maxWorkDate.Ticks;
        }

[0:] GetWorkTimeProgressProcentage - maxWorkDate
[0:] GetWorkTimeProgressProcentage - now (max work date = 01.01.0001 00:10:00)

public double GetWorkTimeProgressProcentage(TimeSpan WorkTime)
        {
            DateTime maxWorkDateTime = StartTime.Add(WorkTime);
            if (DateTime.Now >= maxWorkDateTime)
                return 100;
            if (DateTime.Now <= StartTime)
                return 0;
            DateTime now = DateTime.Now.AddTicks(-StartTime.Ticks);
            return (now.Ticks * 100) / maxWorkDateTime.Ticks;
        }